-LRB- CNN -RRB- -- North Korea 's latest nuclear test , coming on the heels of December 's successful satellite launch , suggests that Pyongyang is moving forward toward developing a nuclear warhead and a deliverable missile system , experts say . The question remains : How close is it ?

The answer , like the cloistered `` hermit kingdom , '' remains largely a mystery , as does much of its nuclear program .

`` It 's a question over the delivery system and the reliability of those systems , '' said Daniel Pinkston , senior analyst for the International Crisis Group covering Northeast Asia . `` That is essentially unknown , or known by a few people inside North Korea . ''

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A 2009 report by International Crisis Group suggests that North Korea `` probably has somewhere between six and twelve nuclear weapons , or at least explosive devices , '' but notes that experts are divided on whether any of these are now usable as warheads -- small enough to be mounted on missiles and durable enough to withstand the hazards of flight .

`` It 's pretty clear that these are advanced technologies and the systems present a number of engineering challenges -- and to master these technologies requires a number of tests , '' Pinkston said .

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In December , on the first anniversary of the death of its former leader Kim Jong Il , North Korea successfully launched a three-stage rocket that put the satellite Shining Star-3 into orbit . The launch also signaled that the North 's long-range missile program now puts the United States within reach .

Last month , the United Nations Security Council unanimously passed a resolution that strengthened sanctions against the North in response to the December rocket launch . Declaring sanctions to be tantamount to `` a declaration of war , '' North Korea threatened further missile and nuclear tests , which it said are a new phase of confrontation with the United States .

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Tuesday 's underground nuclear test is North Korea 's third , following tests in 2009 and 2006 . The test , `` probably '' conducted in the vicinity of P'unggye , yielded `` several kilotons , '' according to assessments cited by the U.S. director of national intelligence .

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Estimates of the size , or yield , of the 2009 nuclear test range from 2.5 kilotons to 6 kilotons , Pinkston said . By comparison , the atomic bomb dropped on Hiroshima had a yield of 16 kilotons .

While the specter of a North Korea able to send nuclear-tipped missiles is worrisome , equally troublesome to the international community is Pyongyang 's atomic technology fueling the black market for weapons .

`` If its clandestine uranium-enrichment program has made strides , Pyongyang could demonstrate that it will gain access to a far larger pool of fissile material than simply its limited supply of weapons-grade plutonium , '' wrote Patrick M. Cronin , an Asia expert at the Center for New American Security , in a CNN op-ed . `` A larger pool of fissile material is a dual threat : As a vital part of an expanded nuclear weapon program and as a commodity to be sold on the black market . ''

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CNN 's Jethro Mullen contributed to this report .

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North Korea says it carried out an underground nuclear test Tuesday

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It is the third nuclear test Pyongyang has carried out since 2006

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It comes after new U.N. sanctions for North Korea 's December satellite launch

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Experts say it 's unknown how close the North is to being able to launch a nuclear warhead